Severe Thunderstorm Warning 317, NWS Denver/Boulder, CO

Area Forecast Discussion
National Weather Service Denver/Boulder CO
253 PM MDT Thu Jul 20 2023

.SHORT TERM...(This evening through Friday)
Issued at 231 PM MDT Thu Jul 20 2023

Strong thunderstorms have already developed over the mountains,
foothills and adjacent plains early this afternoon. These will
continue to develop and spread eastward over the plains through
the evening hours. Severe thunderstorm watch has just been issued
for much of the eastern plains of Colorado with the exception of
Phillips and Sedgwick county until 03z. Instability is improving
with ML CAPE at Denver at 1200j/kg of latest ACARS sounding with
just a small inversion left at 750mb. The scarcity of storms over
the Denver area maybe due to the morning cloudiness and showers
that occurred early this morning. Current precipitable water
values closing in on 1.20" of water with continued threat of very
heavy rain with storms. Expect the deepest moisture farther east
with pw values close to 1.50". Rainfall rates up to an inch in 30
minutes or less is expected with strongest storms.

The features responsible for the severe weather today is an upper
wave now entering northwest Colorado with noted drying occurring
behind the wave across Utah and Nevada. RAP Analysis showing 60kt
speed max slicing across central Colorado. Given latest HRRR showing
a second round storms early this evening from the back edge of the
upper wave this looks like a reasonable solution. Substantial dry
and subsidence kicks in behind the wave with drying and storms
ending from northwest to southeast through the night. Drier airmass
along with warmer temperatures expected for Friday. Looks like
enough moisture for isolated showers/thunderstorms over the
mountains and adjacent plains.

.LONG TERM...(Friday night through Thursday)
Issued at 231 PM MDT Thu Jul 20 2023

An upper level high amplifies while sitting over the Four Corners
this weekend. This pattern will keep northwest flow bringing drier
air into the region. Low levels will have enough moisture Saturday
due to shortwave in the southern Rockies. This could lead to
isolated weak high based showers mainly in the foothills and South
Park Saturday afternoon. These high based showers will likely
produce strong wind gusts and light rain until Saturday evening.
Additionally, without much cloud cover, temperatures will begin to
warm. Parts of the foothills, urban corridor and plains increase
near mid 80s to lower 90s. Mountains and valleys trend near the low
to upper 70s Saturday afternoon. Clear skies continue through Sunday
morning.

Relative humidity across the region decreases near 15-20 percent
for the higher elevations. Northwest winds remain weak near 10-12
mph thus fire weather conditions should remain low. With MLCAPE
near 100 J/kg for the foothills and mountains, decided to decrease
NBM PoPs Sunday keeping less than 20-25 percent for the foothills
and majority of Park County. Additionally, without much cloud
cover, temperatures will begin to warm. Parts of the foothills,
urban corridor and plains increase near mid 80s to lower 90s.
Mountains and valleys trend near the low to upper 70s Saturday
afternoon.

Moisture continues to wrap around the upper level system which
increases our chances for diurnal showers and storms next week. Most
guidance favors the higher elevations for scattered showers and
storms but a stray shower or storm cannot be ruled out for the
Palmer Divide. ECMWF ensembles display increasing temperatures
Monday through Wednesday all areas.  Both GFS and ECMWF ensembles
present KDEN reaching 98-99 for a high temperature both Monday and
Tuesday. With increasing cloud cover

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1137 AM MDT Thu Jul 20 2023

Expect impacts at the terminals this afternoon and evening with possible
two waves of storms, first window from 19-23z and a second shot
of storms from 00-03z. Expect strong/severe storms with large
hail, very heavy rain and strong winds. Expect MVFR cigs/vsbys
with the passing storms. Following the convection, expect a
stratus deck for the night, diminishing by mid morning.

&&

.HYDROLOGY...
Issued at 231 PM MDT Thu Jul 20 2023

Deeper moisture today will enhance the risk of flooding in the
burn scars. Rainfall rates up to an inch in 30 minutes or less
may occur with the stronger storms. Storm motions will be moving
at a decent clip which may help to minimize flash flooding as long
as training storms don't develop. Flash flood watch has been
extended until midnight tonight for the Palmer Divide region,
including Washington county.

The flash flood threat remains little to none over the burn areas
this weekend.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Flood Watch until midnight MDT tonight for COZ046-047-049.

&&

SHORT TERM...Entrekin
LONG TERM...AD
AVIATION...Entrekin
HYDROLOGY...Entrekin/AD

Hazardous Weather Outlook
National Weather Service Denver/Boulder CO
1013 AM MDT Thu Jul 20 2023

COZ030>051-211615-
Jackson County Below 9000 Feet-
West Jackson and West Grand Counties Above 9000 Feet-
Grand and Summit Counties Below 9000 Feet-
South and East Jackson/Larimer/North and Northeast Grand/
Northwest Boulder Counties Above 9000 Feet-
South and Southeast Grand/West Central and Southwest Boulder/
Gilpin/Clear Creek/Summit/North and West Park Counties Above
9000 Feet-Larimer and Boulder Counties Between 6000 and 9000 Feet-
Jefferson and West Douglas Counties Above 6000 Feet/Gilpin/Clear
Creek/Northeast Park Counties Below 9000 Feet-
Central and Southeast Park County-
Larimer County Below 6000 Feet/Northwest Weld County-
Boulder And Jefferson Counties Below 6000 Feet/West Broomfield
County-
North Douglas County Below 6000 Feet/Denver/West Adams and
Arapahoe Counties/East Broomfield County-
Elbert/Central and East Douglas Counties Above 6000 Feet-
Northeast Weld County-Central and South Weld County-Morgan County-
Central and East Adams and Arapahoe Counties-
North and Northeast Elbert County Below 6000 Feet/North Lincoln
County-
Southeast Elbert County Below 6000 Feet/South Lincoln County-
Logan County-Washington County-Sedgwick County-Phillips County-
1013 AM MDT Thu Jul 20 2023

...Strong to severe thunderstorms possible through this evening...

...Flood Watch in effect for eastern Elbert, Lincoln and Washington
counties 2 PM to 10 PM this evening...

This hazardous weather outlook is for northeast and north central
Colorado.

.DAY ONE...Today and Tonight

An active period of thunderstorms will occur through this
evening with storms becoming stronger and more numerous during
the afternoon and evening hours. Some of these storms are expected
to become severe across the plains with hail up to tennis ball
size, damaging wind gusts, very heavy rain, and isolated
tornadoes.

The flash flood threat will be elevated in the burn scars this
afternoon, with the greatest threat of flash flooding expected to
be over Lincoln, Eastern Elbert and Washington counties.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

Thunderstorm activity will decrease Friday with isolated to
scattered thunderstorms. By Saturday, most areas will be dry with
only a few high based showers and storms possible over the
higher terrain. Temperatures will be increasing with highs
reaching the mid 90s Sunday and into early next week.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will be needed across the plains through this
evening.

Special Weather Statement
National Weather Service Denver CO
1049 AM MDT Thu Jul 20 2023

COZ048-050-051-201730-
Phillips County CO-Sedgwick County CO-Logan County CO-
1049 AM MDT Thu Jul 20 2023

...A strong thunderstorm will impact portions of east central Logan,
northwestern Phillips and southwestern Sedgwick Counties through 1130
AM MDT...

At 1048 AM MDT, Doppler radar was tracking a strong thunderstorm 5
miles west of Fleming, or 14 miles northeast of Sterling, moving east
at 30 mph.

HAZARD...Wind gusts up to 50 mph and penny size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor damage to outdoor objects is
         possible. Hail may accumulate on roadways causing hazardous
         travel.

Locations impacted include...
Haxtun and Fleming.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

To report severe weather, contact your nearest law enforcement
agency. They will relay your report to the National Weather Service
office in Denver Colorado.

&&

LAT...LON 4065 10301 4076 10302 4078 10248 4054 10258
TIME...MOT...LOC 1648Z 277DEG 25KT 4071 10295

MAX HAIL SIZE...0.75 IN
MAX WIND GUST...50 MPH

HIRIS

Special Weather Statement
National Weather Service Denver CO
134 PM MDT Thu Jul 20 2023

COZ040-041-045-046-202015-
Elbert/Central and East Douglas Counties Above 6000 Feet CO-
North and Northeast Elbert County Below 6000 Feet/North Lincoln
County CO-Central and East Adams and Arapahoe Counties CO-
North Douglas County Below 6000 Feet/Denver/West Adams and Arapahoe
Counties/East Broomfield County CO-
134 PM MDT Thu Jul 20 2023

...A strong thunderstorm will impact portions of northeastern
Douglas, northwestern Elbert and central Arapahoe Counties through
215 PM MDT...

At 134 PM MDT, Doppler radar was tracking a strong thunderstorm over
The Pinery, or 20 miles southeast of Denver, moving northeast at 25
mph.

HAZARD...Wind gusts of 50 to 55 mph and nickel size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor damage to outdoor objects is
         possible. Hail may accumulate on roadways causing hazardous
         travel.

Locations impacted include...
Southeastern Aurora, southeastern Centennial, northeastern Castle
Rock, Parker, The Pinery, Franktown, Ponderosa Park and northeastern
Castle Pines.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

A Severe Thunderstorm Watch remains in effect until 900 PM MDT for
northeastern and east central Colorado.

&&

LAT...LON 3936 10477 3949 10489 3976 10448 3951 10427
TIME...MOT...LOC 1934Z 240DEG 21KT 3946 10477

MAX HAIL SIZE...0.88 IN
MAX WIND GUST...55 MPH

HIRIS

Preliminary Local Storm Report
National Weather Service Denver CO
216 PM MDT Thu Jul 20 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0213 PM     Hail             4 ENE Ponderosa Park    39.41N 104.57W
07/20/2023  M1.00 inch       Elbert             CO   Trained Spotter

            Spotter: E561.

&&

AD

Preliminary Local Storm Report
National Weather Service Denver CO
255 PM MDT Thu Jul 20 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0250 PM     Hail             4 E Kiowa               39.33N 104.38W
07/20/2023  M1.75 inch       Elbert             CO   Trained Spotter

&&

GH

Preliminary Local Storm Report...Summary
National Weather Service Denver CO
310 PM MDT Thu Jul 20 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0250 PM     Hail             4 E Kiowa               39.33N 104.38W
07/20/2023  M1.75 inch       Elbert             CO   Trained Spotter

0213 PM     Hail             4 ENE Ponderosa Park    39.41N 104.57W
07/20/2023  M1.00 inch       Elbert             CO   Trained Spotter

            Spotter: E561.

0208 PM     Hail             1 NE Ponderosa Park     39.41N 104.62W
07/20/2023  E1.00 inch       Elbert             CO   Public

            Report from mPING: Quarter (1.00 in.).

0123 PM     Hail             2 NW Castlewood Canyon  39.37N 104.80W
07/20/2023  E0.75 inch       Douglas            CO   Public

            Report from mPING: Dime (0.75 in.).

&&